As a method for producing a hollow rod-like body having an optional form and one or more hollow holes from ceramics, metals, or carbon, a method of forming a hollow rod-like body by press molding, cast molding, injection molding, rubber-press method, hot plate press method, or the like, and sintering the molded object or a method of providing a sintered object (rod-like body) with a certain external appearance and drilling a hollow hole through the sintered object by drill processing, electrical discharge machining, electrochemical processing (ECM processing), or the like has been employed.
These methods, however, involve a very complicated process and technical difficulty, resulting in poor productivity. This tendency is particularly conspicuous when narrowing the size of holes or producing hollow holes at a high density.
For this reason, a method of producing a hollow rod-like body (including a honeycomb structural object) having one or more hollow holes by forming a hollow extrusion material by extrusion molding using a special die or a special mouthpiece and sintering the extruded object has been mainly employed in recent years.
This method was successful in greatly improving productivity and optionally selecting the form and number of hollow holes by using a die.
However, since a material with a comparatively low viscosity is used in this method, the hollow holes are easily collapsed after extrusion molding. It has been difficult to constantly maintain a good quality. In particular, to produce a hollow rod-like body (including a honeycomb structural object) having fine hollow holes at a high density has been difficult due to the structure of dies. An additional problem has been a high production cost due to easily worn-out and very expensive dies.
To overcome the above problems, a method for producing a cellular honeycomb has been proposed. The method described in Published Japanese Translation of PCT Publication (WO 99/32777) for Patent Application No. 2001-526129, for example, comprises providing a cellular structure object (honeycomb structure object) containing two or more parallel channels having a predetermined section, filling the channels with a filler, and remodeling the cellular honeycomb structure by narrowing with a taper.
A method for producing a hollow rod-like body with a porous structure has been proposed in Japanese Patent Application Laid-Open No. 2001-247372, for example. The method comprises producing thin hollow rods of ceramic of which the hollow space is packed with a filler, bundling a plurality of such hollow rods and remodelling the bundled rods to form a bundle (optionally, again bundling the formed bundles and remodeling the rebundled objects), and extruding the bundle using a die and a plunger.
Another method that has been proposed by, for example, Japanese Patent Application Laid-Open No. 6-264105, produces a body to be sintered having a helical hole inside the section and a twist groove in the outer circumference. The method comprises extruding a kneaded plastic material from an extruder and causing the extruded material to pass through a torsion-imparting device and then through a metal die to obtain the body to be sintered.
The method of Published Japanese Translation of PCT Publication (WO 99/32277) for Patent Application No. 2001-526129 requires a step of packing and removing the filler after preparing a cellular structural object (honeycomb structural object), giving rise to an increase in the manufacturing cost for the filler and the die for the honeycomb structural object.
The method of Japanese Patent Application Laid-Open No. 2001-247372 has a problem of difficulty in producing rod-like bodies with fine linear holes for fabricating the hollow rod-like body with a porous structure. The method also requires a complicated procedure for remodeling and cannot produce cells at a high density.
The method of Japanese Patent Application Laid-Open No. 6-264105 can produce a hollow structure by extrusion molding, but can neither produce holes at a high density nor arrange the holes in a desired pattern. An additional problem with this method is a high mandrel production cost.
The present invention has been completed in view of the problems in the prior art mentioned above and has an object of providing a forming jig which can easily and inexpensively design or change the design of a forming pattern of hollow holes and the external configuration of a formed body, and can form fine hollow holes at a high density, and a method for producing a formed body using the jig.